Telephone system



May 14, 1940- K. WOLAK TELEPHONE SYSTEM Filed Jill 24, 19s? 3Sheets-Sheet l INVENTOR. K U R T WO L A K .12% Z 4 ATTORNEY. I

May 14, 1940. K. WOLAK TELEPHONE SYSTEM Filed July 24. 1937 3Sheets-Sheet 2 INVENTOR. KURT WOLAK ATTORNEY.

May 14, 1940. K. WOLAK I TELEPHONE SYSTEM Filed July 24, 1957 sSheets-Sheet s INVENTOR. K RT WOLAK Z ATTORNEY.

Patented May 14, 1940 osiiso 2,200,.tii

osiios izsms iomo system Kurt Wolalz, Berlin,

Germany, assi'gmor to Siemens is Halshc Alstiengesellschaft,Siemenss'tadhneai Berlin, Germany 3 Application July 24, 193i. Serial155,423

iii Germany August 31, 1936 11 Claims. (Cl. flaw-3i) The inventionrelates to a circuit arrange ment for telephone systems havingsubscribers stations at which any influencing oi the receiver at aparticular station by the cur-rests produced the microphone of the sa-tion is pc vented by means of a balancing circuit.

As is kaown such arrangements have the advantage that the talking pastyis not disturbed by room noises or by his own speech which areassociated with the subscribers station cording to the invention whichwhena 13a Jar typeof call is established or when a call .18 establishedin a. particular .clirmtion disconnect the balancing circuits at thesubscribers stations whichare connected together and ,conneotthereceivers micmphonesv to the subscribers lines iii-circuits which areindependent of one another.

Fig. .1 shows a linehaving plurality .of .sub..- stations embodying theinvention.

Fig. 2 shows a switching system in which the balancing circuits at thesubstations are out in dependent upon theestablishmeiit of calls in aparticular direction. l

Fig. 3 shows the circuit of a local battery subqscribers station.

14 is'a further modificationv skeleton form zshowing the switches iorextending a connection between two substations.

5 shows the modified arrangement inwliich two groups of groupseleotorsazte show-o.

The attached figures show embodiments of the invention. Only thosedetails are shown which are necessary to enable the invention to beunderstood.

Fig. 1 shows an arrangement in which't hebale arising circuit isswitched over at the subscribers stations in 'dependenceopon theparticular type of call, for examples conference call; In Fig". .1 aline circuit is represented having subscribers I, Il. and 1:11. ,All thesubscribers stations aroconstructed in identical manne-r; ,All thecircuit details are shown at soioscribess stations in the known mannerso that themicrophone II. The references "are the same at all thestations. Individual calls can be set up between two suo riioersiahdalso conference calls in which any pa zlar "subscriber can connect theother subscribe 5 together ina conference call. When 5 conference callis set up an amplifier V-st comto. all the stations connected. up.

The establishment of an individual call will first "be described. Ifsubscriber 'I for example desires connection to subscriber I1 he setshis 10 selecting device, of which the wiper o, is shown, on the contactassociated with the desired sub- "her Whenthis has taken place he 'du" rcsses 'calii g key RT and ther'elsy closes the circuit ifol l indicatingsignal at the callealsub- U at-ion: earth, hatter-y, cal-ling lacy RT tothe right) d, leacl t, wiper d at station II, calling liey'RT in therest position, switchhook cohtacthui, indicating signal ElZl and earth.i i I At the called subscribers station 11 an indicator is operated andthe subscriber takes up hisreceiver and thereby closes the contactsmill,

frail, hu l, hue, hul and Mia operated co the switchho'ok. At the sametime contact iwi is opened. contact hul a seized lamp Bel is swi'tolledon at the called subscribe-rs station.

takes up receiver after restoring the calling key RT to the left-handposition and thereby similarly closes the contacts h'iLQ, 7221.3, hu l,hut and 122123 Here also at contact hot? the transformer =Uc2'iscoi-mectecl over the calling key RT in the rest position and wipes oi tolead 6. The seizes lamp Bel is-switched on at the calling station bycontact hw'l, furthermore, the microvphonefeeding circuit is completedby contact .imt. operation of the other contacts of the switchhook iswithout significance. Converse..- tion can :now take place. The speechcurrents at bothstations pass over the speech trahsfoifmer Ue. Thecircuit of the transformer is arranged '50 which is fed from a localsource, coupled inductively over a winding III to the windings I I and"II of the transformer whichare connected tothe lead Winding IIis inseries with a halancinscoil Thetelephone'l is connected .55

between the two windings I and II. of the transformer. The transformeris accordingly in the known form of a bridge circuit in a diagonal ofwhich the telephone T is disposed. It serves the purpose of keeping themicrophone currents from the talking partys receiver.

The connection is released on the replacement of the receiver at the twosubscribers stations and restoration of the line switch to normal at thecalling station.

If a subscriber, for example, subscriber I, wishes to establish aconference call in which all the subscribers connected to the system areto be connected together, he depresses the key GT. In consequence therelay R is energized at each station in the followng circuit: earth,battery, choke-coil Dr, key GT, lead 3, the branch lead to the R relaysat each subscribers station, contact ha? of the switchhook, the windingsof the relays R and earth. Relay R energizes at each station. Contact rlis opened and contacts 12 -to T are closed. Contact r5 operates a visualsignal SZZ at each subscribers station. Through the opening of contact1! the telephone T is disconnected from the windings of the transformerat each station and thereby disconnects the telephone T from the bridgecircuit. By means of contact T2 the telephone T at all the subscribersstations is connected directly to the common line i. The incoming speechcurrents since they are no longer damped can pass in amplified formthrough the receiver.

When after the visual signal has been operated the receivers are takenup themicrophones M which are inductively coupled to windings I and IIof the transmitter are connected to the common lead 3 over contacts 14and hu l. The microphone currents also pass to the line in amplifiedform since the bridge circuit involving a diminution of current isremoved. i

' Through the opening of contact hu5 the relays R! of the stations aredisconnected from the common lead 3. The relays lock up, however, over:earth, winding of relay R, contact 13, switchhook contact hu6, batteryand earth. When all the subscribers have taken up their receivers thefollowing circuit is closed over the opposing winding I of all thevisualsignal relays SZ2 at the stations: earth,.battery, lead 2,switchhook contact hufl at station I, winding I of the visual signal SZ2at station I, switchhook contact hu8 and winding 1 of the visual signals$22 at stations II and III and earth. The visual signals at the stationsare restored through the operation of the counter-winding. This servesto indicate to the callingstation that all the stations which have beencalled for the conference, have replied.

To lead 3 there is also connected a relay RV in addition to the relays Rat the individual stations and this-is associated with the amplifier Vstwhich is common .to all the subscribers stations. Through the closing ofthe conference call key GT at the calling station I this relay also isenergized over: earth, battery, choke-coil Dr, key GT, lead 3, windingof relay RV and earth. Relay RV closes its contacts re and therebycompletes the striking circuit (indicated diagrammatically) for theamplifier Vst. The amplifier is thus ready for operation.

Since the lead 3 to which all the microphone circuits of the individualstations are connected passes over the primary winding? of the inputtransformer EUe, and lead I to which the telephones of all thesubscribers stations are con nected passes over the secondary winding Sof the output transformer Aue of the amplifier Vst all the microphonesand telephones are coupled together over the amplifier. The subscriberscan converse together over the amplifier Vst.

The conference call is released in that the conference call switch GT isrestored in the calling station I whereby relay RV releases anddisconnects the amplifier. Through the receivers being replaced at thestations the locking circults for the relays R. are opened and thetelephones T are again connected to the junction between windings I andII of the transformers. Through the opening of the switchhook contacthu3 the microphone feeding circuits at all the stations are broken. Theremaining contacts of the switchhook re-establish the normal conditionto enable the establishment of individual calls.

Fig. 2 shows an arrangement in which the balancing circuits at thesubscribers stations which are connected together are switched over independence upon. the establishment of' calls in a particular direction.

It will be assumed that subscriber Ta. wishes to set up a connection ina direction in which the balancing circuit is to be switched over. Hetakes up his receiver, thereby closing the switchhook contacts hul andM42. A line relay in the preselector-VW associated with the callingsubscrib-' ers line is thereby energized over the completed loop in theknown way. The preselector is set in operation and searches for a freeline leading to a first group selector GW. The circuits have no bearingon the invention and are, therefore, not shown. When the preselector VWhas found a free line the relays AI and Bi energize in the groupselector GW over the subscribers loop.

Relay Vl is energized over: earth, contact 80,

winding of relay VI, contact Ial, battery and earth. The testingrelay'Pr of the preselector and the seizingrelay C of the first. groupselector are energized over the testing lead of the impulses for settingthe group selector GW by means of his dial switch. Four levels of thegroup selector are indicated in the drawing. Over preselector VW.Subscriber Ta. now transmits I level 3 pass calls in which switchingover is to take place at the subscribers stations while over' level 4,for example, connections are set up in other directions'in which noswitching over of the subscribers circuits takes place. Thecharacterizing number for the traffic directions vin which the balancingcircuits have to be switched over at the subscribersstations is'thus thedigit 3. The subscriber first transmits an impulse train of threeimpulses which are transmitted over the receivingrelay Al to the groupselector vertical magnet in the known way. The group selector is set onthe third level. At; the-end, of the vertical motion it searches freelyfor a' line leading to a further group selector or as indicated in thefigure directly to a final selector LW.

A discriminating device in the form of a rotary switch is associatedwith the group selector GW,

the rotary magnet Dm and the wiper dmbeing shown. When the groupselector isset by the first impulse train the discriminator is also seton the'contact 3, this taking place in the following way: I i

Whenrelay Al falls back. for the first time ref 12.9 V2 energizes.Relay. V2 is short-circuited impulsively during the impulsingat contactfal and holds up on account of its slow-to-release feature. -WhenrelayAl energizes againfor the first time the following circuit is completedfor the rotary magnet Dm of the discriminator:

earth, the winding of the rotary magnet .Dm, contacts da t, 23.222 and32a, battery and earth. The rotary magnet of the discriminator isadvanced this way to contact 3. At the end of theimpulse train relay V2is again short-circuited by contact in! so that it releases and nowcloses the following circuit for relay .X: earth, contact 4'02, wiperrim of the discriminator in position 3, winding of the slow relay X,winding I of relay II, battery and earth. Relay U locks up over: earth,contacts 390., 31a, winding II of relay U, battery and earth. Throughthe opening 01' con-- tact 32a the original energizing circuit of therotary magnet'Dm is broken. Relay X at contact 'lzcclosesthe circuit forthe slowrelay Y. At contact ilx relay X closes a circuit for winding IIof relay Al, An impulse is thus induced for winding I of relay Al andpasses to earth over lead a of calling subscribers line, wiper'a of thepr'ese'lector the glow lamp GL, relay Ra,

lead hof the subscribers line, wiper b of the preselector VW, and thewinding of relay 'Bl. Relay Rava t station Taihas energized by thisimpulse.

At the end of this impulse the armature of relay Rd is :held in theoperated position mechanically :in dependence upon the switchhook orswitchhoolr pin in any known way. The locking of the relay is onlyreleased againwhen the receiver is re placed. Relay Pa opens itscontacts Him, Hm

and 14m and closes its contacts lira, lira and 15m. llhrough the openingof contacts Him and Mm the microphone M at the subscribers station whichis-disposed in parallel with winding I and the halancing-eleznentisdisconnected from the speech transformerllr and is connected directlyacross the speaking leads at contact 5.2m and I5ra. The-receiver T atstation Ta which is inductively coupled to windings I and II of thespeechtransiormer overwinding III of the trans former connected :acrossthe speaking leads over contact 15m and. the 'swit'chhook contact huZthe balancing element N being disconnected at the same time. Thus theshunt constituted by winding I of the transformer and the balancingelement N is disconnected as regards the outgoing currents from themicrophone M. The incoming speech currents are also less damped in theirpassage to the telephone '1 on account of the disconnection of thebalancing element N.

The embodiment represents a system having central battery feeding. Theswitching operations can, of course, also be applied in local batterysystems. Fig. 3 represents the circuit for a local battery subscribersstation. Winding I of relay Ra is energized by the induced impulse andby closing contacts 56m and Elm connects the telephone and microphonedirectly across the speaking leads. At the end of the induced impulserelay Ra holds up over a second winding inthe following circuit: earth,switchhook contact l9hu, contact l8m,'winding II of relay Ra, batteryand earth.

In the group selector GW (Fig. 2) relay X completes a circuit for therotary magnet Dm over contact 53:. The discriminator takes a furtherstep and is thereupon advanced to normal over an interrupter which isnot shown. Relay X thereupon releases, relay Y holds up after therelease of relay X in the following circuit: earth, winding of slowrelay Y, contacts my and 3m, battery and earth.

After the reception of the first impulse train the group selector GWsearches freely for a free line. When such a line has been found thetesting relay P energizes over wiper c of the group against furtherseizure.

. selector in the known way. Relay :P ihri'ngs'the :group (selector torest and guards the called line In the linal selector LW the seizingrelay C is energized in the normal way. After the energizing of relay Pin the first group selector the following circuit is set up for relay:P-l: earth, contacts Hip and Elly, winding of relay Pl, battery andearth. Relay Pl energizes and closes the following circuit for winding Iof. the transformerlle: earth, contacts dl-pl 22y, winding I of thetransformer Us, battery and. earth. On account of the closing of thiscircuit an impulse is induced :in winding II p1 the transformer Us whichenergizes relay K in the final selector LW over lead 1): earth, windingII of the transformer Ue, winding of relay M, contacts 23 and Mp3, wiperh of the group selector GW, glow lamp Gil, winding 1 oi slow relay It,battery and earth. In this circuit relays M and Kenergize. Relay Minthegroup selector GW opens its contact 'Em and thereby breaks thelocking circuit for relay Y. Relay Y releasesland thus :opens thecircuit for winding I and II of the transformer Ue. This terminates theinduced impulse. circuit for relay P! at contact 26y.

Relay It. is energized by the induced impulse in the final selector LWas already mentioned. Relay K holds up after the termination of theinduced impulse in the following circuit: earth,

contact 2574:, winding II of relay K, contact 2552, battery and earth.In addition relay K connects winding II of a transformer Ue2 across thespeaking leads by closing its contact 21k. Furthcrm-ore, relay K byclosing its contact 28k pregized the following circuit is set up forwinding I of the transformer Ue2: earth, contacts 28k and 2%2, winding Iof the transformer 'Ueil, battery and earth. An impulse is therebyinduced in winding II of the transformer Tile? and by way of glow lampG1 and relay Ra disposed in series therewithefiects the switching overof the balancing circuit provided for normal calls at the subscribersstation Tb in the same way as in the case of the calling subscribersstation. The circuits completely correspond to those of the callingstation Ta and will not therefore-be described separately. After theenergizing of relay B2 in the final selector LW the locking circuit forwinding II of relay K is .broken by the opening of contact 261:2 relay Kreleases and thereby on the one hand disconnects winding II of thetransformer Ue from across the speaking leads and on the other handbreaks the normal circuit through "the Winding I of the repeater Ue2.

The connection is released in the known way through the replacement ofthe receiver at the calling subscribers station. The replacement of thereceiver at station Ta releases the mechanical locking of relay Ra.Relay Ra releases and reestablishes the originalbalancing circuitbetween the microphone, receiver and transformer. On account of theinterruption of the subscribers loop relays Al and BI in the groupselector GW release. Thesebringsabout the release .of the preselector VWand'therel'ease of the group selector Relay Y in addition breaks the andafter the called subscriber has replaced his,

receiver the release of the final selector LW. The circuits for thisoperation do not concern the invention and accordingly are not shown.

In Fig. 2 the criterion for the switching over of the receiver andmicrophone circuits comprises an induced impulse transmitted fromthe'first group selector to the calling and to the called subscriber.Naturally other arrangements for transmitting this criterion arepossible.

Fig. 4 shows a further embodiment. All unimportant details are omittedfrom the figure. In the group selector GW in place of a discriminator arelay Pi is provided in the testing circuit of the group selector inaddition to the testing relay P and this promotes the transmission ofthe switching criterion to the subscribers station. This relay Pl canonly energize in the testing circuit when the group selector GW is seton a particular level. This level may for example be the level I. To thecontacts of this level are connected the seizing relays C of the finalselectors as is shown in the figure. To the contacts of the otherlevels, for example level 2, the seizing relays C are likewise connectedbut with a resistance Wi in series which prevents the additional relaysPl from energizing. If after being seized by the calling subscriber Ta,the group selector GW is set on level i relay Pl energizes. Moreover,when the switch is set on level I a socalled level contact (170 isclosed by the switch. After the group selector has found a free line theadditional relay Pl energizes in the testing circuit in addition to thetesting relay P and the seizing relay C. Relay Pl opens its contacts42p] and Mpl and closes its contacts 43p! and 45pl. The direction of thecurrent to the subscribers line is thereby reversed. The polarized relayR which is disposed across the speaking lines at the subscriber'sstation energizes in response to this reversal of current. Relay Rdisconnects itself from the subscribers line at its contact 461 but isheld operated until the end of the call, for example, by a mechanicaldevice in dependence upon the switchhook.

In the group selector GW relay Pl closes the following circuit forwinding I of the transformer Ue: earth, winding I of transformer Ue,

level contact dlc, contact iflpl, battery and earth. An impulse isthereby induced in winding II of the transformer Ue which since contact4| pl opens after contact Mlpl is transmitted over the glow lamp GI I towinding I of relay K of the final selector LW: earth, Winding II of thetransformer Ue, contact 4 lpl, wiper b of the first group selector, glowlamp GLI, winding'I of relay K, battery and earth. After the terminationof the impulse relay K holds up over earth, contact 41k, winding II ofrelay K, contact 48b2, battery and earth. Relay K opens its contacts 49kand 5H6 and closes its contacts 50k and 52k. Afiter the final selectorhas been set on the called subscribers line the subscriber is rungagain. When he takes up his receiver the feeding bridge relays AZ and B2in the final selector are energized over the completed subscriber'sloop. After relay B2 has energized the circuit for winding II of relay Kis broken by the opening of contact 48212 and relay K releases andaccordingly opens its contacts 50k and 52k and closes its contacts 49kand Elk. Current is thus reversed back to the called subscribers line.The polarized relay R at station Tb which corresponds completely to thepolarized relay R at the station Ta energizes in response toizhisreversal of .current and in the same'way' as at station'Ta efle'c'ts'theswitching over of the microphone and receiver circuits.

Calls are also set up from difierent groups of subscribers disposed indiiferent exchanges. Since the various groupsof subscribers areconnected in a common multiple over the group selectors subscriberswhich do not require any switching over at their stations can also bringabout such switching by dialling the corresponding characterizingnumber. In order to avoid this the arrangement according to Fig. 5 canbe provided. v

In Fig. 5 two groups of group selectors are shown to which correspondinggroups of subscribers have access. "Only the testing wipers of the groupselectors, indicated bythe reference c, are shown. The contacts I, IIand III indicate the various levels of the group selector over whichdifferent directions are reached. The criterion for the switching overof the subscriber's station circuits is indicated in the same way as inFig. 4 by an additional relay Pl in the testing circuit of the groupselector. As is also shown in Fig. 4 the operation of this additionalrelay PI is dependent upon the resistance in the seizing circuits whichare reached over the various levels in the group selectors. I

In the case of a call from the select'orgroup A in the level I whichcorresponds to a particular direction, relay PI of the seized groupselector of group A is energized together with the testing relay sincethe only other resistance in' the seizing circuit is relay C, and thusbrings about the switching over of the subscribers station circuit.

Switching over of the subscribers station circuits also takes place inthe case of a call from the selector group B in the direction I'as isshown in the figure.

In the case of a call from the selector group A in the level IIcorresponding to another direction, relay Pl does not energize onaccount of the additional resistance Wil in series with the seizingrelay 0 so that no switching over takes place at the correspondingsubscribers station.

The same is true in the case of a call from the selector group B in thedirectionII.

In the case of a call from the selector group A in the level IIIcorresponding to a third traffic direction, relay Pl again efi'ects aswitching over of the station circuits on account of the seizing relay Cbeing disposed Without other resistance in the seizing circuit, but inthe case of a call from the selector group B in the direction III noswitching over of the station circuits takes place since an additionalresistance Wz'2 isv insertecl between the bank contact of the level IIIof the seized selector and the multiple.

Finally it may be mentioned that the invention may be applied not onlyin the case of conierence calls, constituting a special type of call,but also for example in the case of distant calls. The switching over ofthe station circuits can thus be effected in dependence upon the longdistance criterion which is transmitted on long sive switching means atthe station automatically operable only in certain calls from saidsubstation for rendering said side tone preventing means ineffective.

2. In a telephone system, a substation, means for extending differentconnections therefrom, said substation normally connected for side toneprevention, and electro-responsive means in the substation automaticallyoperated only when certain connections are extended therefrom forchanging the connections at the substation to remove the side tonepreventing connections.

3. In a telephone system, a substation normally connected to preventside tone in the receiver, means for extending connections therefrom andfor establishing conference calls therefrom and a relay in thesubstation automatical- 1y operated to change the substation fromantiside tone to side tone whenever conference calls are made therefrom.

4. In a telephone system, a pair of substations each normally connectedto prevent side tone in the receivers by currents generated by theassociated transmitter, and means in each substation automaticallyoperated when a connection is extended from one to the other forchanging the connections in the associated substation so they are notconnected to prevent side tone.

5. In a telephone system, a substation, the transmitter and receiver ofsaid substation normally connected to prevent side tone in the receivercaused by currents generated in the transmitter, automatic switches forextending connections therefrom, and means in the substation, controlledfrom the automatic switches, for changing the connections in thesubstation so as to permit side tone.

6. In a telephone system, a substation, a relay in the substation forchanging the connections thereof, means for extending a talking circuittherefrom, and means for transmitting an induced impulse over saidtalking circuit to operate said relay.

7. In a telephone system, a substation, a relay at the substation forchanging the connections of the transmitter and receiver in saidsubstation, means for extending a connection to said substation, andmeans for transmitting an induced impulse to said substation over saidconnection to operate said relay.

3. A telephone system as claimed in claim 7 in which said relay isconnected to said substation through a glow lamp.

9. A telephone system as claimed in claim 6 in which said relay is heldoperated after the termination of said induced impulse.

10. In a telephone system, a substation, a relay at the substation forchanging the connections of the transmitter and receiver to saidsubstation, means for extending connections from the substation, meansfor operating said relay only when certain connections are extended, theoperation or non-operation of the relay dependent on the trafficdirection in which the connection is extended.

11. In a telephone system, substations, a relay in each substation forchanging the connections of the transmitter and receiver therein, meansfor extending connections to and from said substations and means foroperating the relay at a substation, where either the line is calling oris called, said relays being operated in each instance by a reversal ofthe direction of current flow therein.

KURT WOLAK.

